TW201826807A - Lateral mode capacitive microphone - Google Patents

Abstract

The present invention provides a capacitive microphone including a MEMS microphone. In the microphone, the movable or deflectable membrane/diaphragm moves in a lateral manner relative to the fixed backplate, instead of moving toward/from the fixed backplate. The squeeze film damping is substantially avoided, and the performances of the microphone is significantly improved.

Description

Capacitive microphone in landscape mode

The present invention relates to a condenser microphone in a horizontal mode. The microphone of the present invention can be applied to public broadcasting systems of smart phones, telephones, hearing aids, concert halls and public places, film production, live and recording engineering, two-way radio, expansion Sounders, radio and television broadcasts, and voice recording, voice recognition, VoIP, and non-acoustic purposes such as ultrasonic or knock sensors in computers.

A microphone is a sensor that can convert sound into an electronic signal. Among different designs of microphones, the composition of condenser microphones or pure condenser microphones is a conventional structure using a so-called "parallel plate" capacitor design. Other types of microphones with more power are different. In the condenser microphone, only a very small mass needs to be moved by the incident sound wave. The condenser microphone usually produces high-quality sound signals, and is now widely used in consumer electronics, laboratories And studio applications, from phone transmitters to cheap karaoke microphones to high-fidelity recording microphones.

Figure 1 is a schematic diagram of a parallel condenser microphone in the conventional technology. The two thin layers 101 and 102 are arranged close to each other in parallel, one of which is a fixed back plate 101 and the other is moved or driven by sound pressure. Movable / deformable film / diaphragm 102, which is one of the flat plates of the capacitor, and its vibration will change the distance between the layers 101 and 102 and change the mutual capacitance between them.

"Extruded film" and "extruded film" refer to the type of hydraulic or pneumatic damper used to dampen the vibrational movement of a moving part relative to a fixed part, when the moving part moves vertically and approaches the surface of the fixed part (for example, in (Approximately 2 to 50 microns), damping by a squeeze film occurs, and the squeeze film effect is caused by a compressed and expanded fluid (such as a gas or liquid) trapped in the space between the moving plate and the solid surface As a result, the fluid has a high resistance and prevents the movement of the moving parts when the fluid flows through the space between the moving plate and the solid surface.

In the condenser microphone shown in FIG. 1, when the layers 101 and 102 are relatively close to each other and air is kept between them, squeeze film damping occurs, and the layers 101 and 102 are relatively close (for example, within 5 μm). The air is "squeezed" and "stretched" to slow down the action of the film / diaphragm 101. Since the gap between the layers 101, 102 is shortened, the air must flow out of the area. Therefore, the air flowing The viscosity creates a force that resists the movement of the film / diaphragm 101. When the film / diaphragm 101 has a large surface area to gap length ratio, the squeeze film damping will be obvious, and the squeeze film damping between the layers 101, 102 will become a mechanical noise source, and The dominant factor among all noise sources in the overall microphone structure.

The invention effectively provides a microphone design, which can substantially avoid squeeze film damping, because the movable film / diaphragm does not move toward the fixed back plate.

The invention provides a condenser microphone, which comprises a first conductor and a second conductor, and a relative spatial relationship is arranged between the two conductors, so that a mutual capacitance is generated therebetween. Both the relative spatial relationship and the mutual capacitance are changed by a sound pressure that strikes the first electrical conductor and / or the second electrical conductor in a range along an impact direction in a three-dimensional space. Based on the same force / strength of the sound pressure, the maximum mutual capacitance (or the maximum mutual capacitance) can be generated by striking the sound pressure of the first electrical conductor and / or the second electrical conductor along one direction within the above-mentioned collision direction range. Ground change), this direction is defined as a main direction. The first electrical conductor has a first projection along the main direction on a film plane perpendicular to the main direction, and the second electrical conductor has a second projection along the main direction on a conceptual plane; wherein the There is a shortest distance Dmin between the first projection and the second projection, and whether or not the first conductor and / or the second conductor is impacted by a sound wave along the main direction, the shortest distance Dmin is greater than 0.

The previously disclosed features and effects and other features and effects of the present invention can be quickly understood from the following detailed description of the preferred embodiments of the present invention combined with the accompanying drawings.

For the purpose of explanation, many specific details are provided in the following description in order to thoroughly understand the present invention; however, for those of ordinary skill in the art, the present invention is implemented without these specific details or in equivalent configurations. It is obvious.

Where a numerical range is disclosed herein, the range is continuous unless otherwise indicated, and includes the minimum and maximum values of the range, and each value between the minimum and maximum values; additionally, In the case where the range is an integer, only integers from the minimum value to the maximum value of the range are included; in addition, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined.

FIG. 2A shows a condenser microphone, such as a micro-electromechanical (MEMS) microphone, according to different embodiments of the invention. A first conductor 201 and a second conductor 202 are arranged with a relative spatial relationship, so that a mutual capacitance is generated therebetween. The first conductor 201 and the second conductor 202 are independent of each other and are made of polysilicon, gold, silver, nickel, aluminum, copper, and chromium. (Chromium), titanium (titanium) and platinum (platinum), the relative spatial relationship and the mutual capacitance can be changed by the sound pressure of the first conductor 201 and / or the second conductor 202 . As shown in FIG. 3, the sound pressure can strike the first conductive body 201 and / or the second conductive body 202 along a range (shown by a dashed line) in an impact direction in a three-dimensional space. Strength / strength, the mutual capacitance can be changed to a maximum through the sound pressure of the first conductor 201 and / or the second conductor 202 in a specific direction along a range of impact directions as shown in FIG. 3 ( The biggest change), the change of the mutual capacitance (DMC) caused by different impact directions from the sound pressure in the three-dimensional space with the same intensity (IDAPWSI) is shown in Fig. 4. A main direction is defined as the impact direction. In order to generate the peak value of the mutual capacitance (DMC), that is, the direction 210 indicated in FIG. 2A, it can be further understood that, based on the same force / intensity of the sound pressure, the relative spatial relationship can be determined by an A specific direction X in the range of impact on the first conductor 201 and / or the second conductor 202 changes the maximum (or maximum change) sound pressure. The direction X may be different from the main direction as defined above. Direction 210 is the same or different, in In the same embodiment of the present invention, the main direction may be alternatively defined as the direction X.

Referring back to FIG. 2A, the first electrical conductor 201 has a first projection 201P along the main direction 210 on a conceptual plane 220 perpendicular to the main direction 210, and the second electrical conductor 202 has a conceptual plane There is a second projection 202P along the main direction 210 on 220e, and there is a shortest distance Dmin between the first projection 201P and the second projection 202P. In the present invention, the shortest distance Dmin may be constant or variable, but constant It is greater than 0, regardless of whether the first conductive body 201 and / or the second conductive body 202 are hit by a sound wave along the main direction 210. FIG. 2B shows an exemplary embodiment of the microphone of FIG. 2A. The first conductor 201A is immovable and has a function similar to a fixed back plate of a conventional technology, similar to the film / diaphragm 102 in FIG. 1, and the second conductor 202. A large flat area of the receiving sound pressure, and move up and down along the main direction perpendicular to the flat area; however, the conductors 201 and 202 are arranged in a side by side spatial relationship, as one of the "flat plates" of the capacitor, The second electrical conductor 202 does not move toward and from the first conductor 201, but instead the second conductor 202 moves laterally or "slides" on the first conductor 201, so that the first conductor 201 and the second conductor The overlapping area between the bodies 202 changes, and therefore the mutual capacitance therebetween. Based on the relative movement between the first and second conductive bodies 201, 202, this is referred to as a lateral modal microphone in the present invention.

In the exemplary embodiment of the present invention, the microphone may be a MEMS (Micro Electromechanical System) microphone, also known as a chip / silicon microphone, which is typically a pressure-sensitive diaphragm. The MEMS process technology is directly etched on the silicon wafer, and is usually accompanied by a preamplifier integrated circuit. For a digital MEMS microphone, it may include an analog digital converter (ADC) circuit built on the same CMOS chip, making the chip a digital microphone, which can be easily integrated with digital products.

In the embodiment shown in FIG. 5, the condenser microphone 200 may include a substrate 230, such as a silicon substrate. The substrate 230 may be regarded as a conceptual plane 220 shown in FIG. 2A, the first conductive body 201 and the second The conductive body 202 may be constructed in parallel on the substrate 230, or as shown in FIG. 5, the first conductive body 201 surrounds the second conductive body 202. In an exemplary embodiment, the first electrical conductor 201 is fixed relative to the substrate 230; in the other direction, the second electrical conductor 202 may be a thin film and is movable relative to the substrate 230, the main direction Is perpendicular to the film plane 202, and the movable film 202 can be set on the base plate 230 via three or more suspensions 202S (for example, four suspensions 202S). As described later, each suspension 202S can include With foldable and symmetrical cantilever.

In the embodiment shown in FIG. 6, the first conductive body 201 includes a first comb tooth group 201f, and the movable film as the second conductive body 202 includes a second comb tooth surrounding the film peripheral area. Group 202f, the two comb tooth groups 201f, 202f are interlaced with each other, the second comb tooth group 202f moves relative to the first comb tooth group 201f along the main direction perpendicular to the film plane 202; To reduce the air resistance in the gap between the film 202 and the substrate, for example, the squeeze film damping is reduced by 25 times. In a preferred embodiment, the first comb tooth set 201f and the second comb tooth set 202f have the same shape and size. As shown in FIG. 7, each comb tooth has a measurement along the main direction 210. The same width W and the first comb tooth group 201f and the second comb tooth group 202 have a position difference PS along the main direction 210 when there is no vibration caused by sound waves. For example, the position difference PS along the main direction 210 may be a third of the width W, PS = 1 / 3W, in other words, the first comb tooth group 201f and 201f The second comb tooth group 202f has an overlap of two thirds of the width (2 / 3W) along the main direction 210.

In an embodiment, the movable film 202 may have a square shape. As shown in FIG. 8, the condenser microphone of the present invention may include one or more movable films; for example, arranged in a 2 × 2 array configuration. Made of four removable films.

In the embodiment shown in FIG. 9, the condenser microphone of the present invention includes one or more airflow restrictors 241 to restrict the inflow / outflow in the gap between the film 202 and the substrate 203. The air flow rate, in order to allow air to flow in / out, the air flow limiter 241 is designed to reduce the size of the air passage 240, or the length of the air passage 240 of the air flow limiter 241 may be increased to allow air to flow in / Outflow gap. For example, the air flow restrictor 241 may include an inserting member 242 inserted into a groove 243, not only reducing the size of the air passage 240, but also increasing the length of the air passage 240.

As shown in FIG. 6 and FIG. 7, the comb tooth 201F is fixed on the anchor, and the comb tooth 202f is connected to the diaphragm-shaped second electrical conductor 202 (hereinafter referred to as the diaphragm 202). With vibration, the comb teeth 202f will be linked to the film 202, and the overlapping area between two adjacent comb teeth 201f, 202f will change along this movement, so that the capacitance will also change; eventually the same as the traditional condenser microphone is detected Signal of capacitance change.

Leakage has always been a major issue in the design of microphones, and in the conventional parallel flat design shown in Figure 1, it has small holes around the edges to allow air to pass slowly, thereby keeping the sides of the film 101 at Air pressure balance at low frequencies would be an ideal leak. However, larger leaks are not ideal, because larger leaks will allow some low-frequency sound waves to easily pass through the small holes and be easily detached from the film vibration, making the sensitivity weakened at low frequencies. As shown in FIG. 10, the sensitivity is weakened due to leakage at low frequencies. For a typical condenser MEMS microphone, the frequency range will fall between 100 Hz and 20 kHz, so it is not desirable to reduce the sensitivity as shown in FIG. 10.

In order to avoid large leakage, a better structure as shown in FIG. 9 is designed, which shows a leakage prevention groove or groove and wall. Please refer to FIG. 9 again. The air flow limiter 241 can be used as a microphone in the present invention. One of the structures for preventing gas leakage, the gas flow restrictor 241 includes an insert 242 inserted into the groove 243, which can not only reduce the size of the airflow channel 240, but also increase the length of the airflow channel 240. In the MESM microphone, a deep groove can be etched on the substrate and surrounds the edge of the square film 202, and the wall 242 formed by the deposition connected to the film 202 is formed into a narrow air tube 240 to provide a loud sound Figure 11 depicts the frequency response of leakage prevention. The leakage prevention structure has a significant effect in keeping the frequency response poles flatter in the range of 100 Hz to 1000 Hz. The level of the air resistance can be determined by the groove etched on the substrate. Deep control, deeper grooves have higher impedance.

In the following, a preferred embodiment of the invention can be analyzed through some theories and models; however, this is only to understand the invention, and the invention should not be limited by any particular theory or model.

The pressure noise N _P can be defined as: [Mathematical formula 1]

among them At 300k ( ) Boltzmann constant, For the whole system's sound resistance and Is the area of the film.

Sensitivity and signal-to-noise ratio (SNR) are two of the most important factors describing microphone performance; according to standard calculations, a sound pressure of 20µPa is marked as a sound unit or 0 dB. [Mathematical formula 2]

When there is only one sound unit, the sound intensity in dB will be 0, but if there is a 50,000 sound unit equivalent to 1 Pa sound pressure, the sound intensity in dB will be 94dB, which is equivalent to noise The signal strength (ENL) is usually used to indicate the noise level in a 1Pa environment, so the signal-to-noise ratio SNR can be derived as: [Mathematical formula 3]

The effectiveness of an embodiment of the lateral modal microphone according to the present invention has been identified and evaluated, and is listed in Table 1. Based on the small squeeze film damping, the equivalent noise intensity (ENL) of a single film can be reduced by 4dB. In addition, the four-chip array can also reduce the noise by twice (ie 6dB); therefore, the final signal-to-noise ratio SNR will also be improved by 10dB. [Table 1]: The new lateral modal microphone (new microphone) and the conventional parallel plate microphone (existing microphone) of the present invention

For comparison of frequency response, the lateral modal design has a higher Q factor due to lower damping, as shown in Figure 12. However, because the leakage level is still not low enough, it also has a large sensitivity range from 10kHz to 100Hz at the same time. For comparison, Figure 13 reveals the frequency response of the existing microphone design.

In order to have a more flat frequency response curve, a leak prevention groove or wall or even a double groove can be used in the microphone structure, and the design can be modified by adding one or more grooves / grooves. As shown in the lower diagram of FIG. 9, the double slot can significantly improve performance, as shown in Table 2 below. [Table 2]: The effectiveness of the double tank leak prevention design

In summary, many embodiments of the present invention can be described with reference to many specific details that have changed as the implementation; therefore, the description and drawings should be considered illustrative rather than limiting; and the scope of the invention The exclusive and exclusive indicators, and the scope of the invention that the applicant wants, are the wording and equal scope of a set of patent application scopes, where the set of patent application scopes are in a specific format and announced, and include any subsequent amendments .

102‧‧‧ diaphragm

201, 201A‧‧‧First Conductor

201f‧‧‧first comb set

201P‧‧‧First projection

202‧‧‧Second Conductor

202f‧‧‧Second Comb Set

202P‧‧‧Second Projection

202S‧‧‧ Suspension

210‧‧‧ Main direction

220, 220e‧‧‧ Concept Plane

230‧‧‧ substrate

240‧‧‧air passage

241‧‧‧Air flow limiter

242‧‧‧ Insert

243‧‧‧Groove

The drawings illustrate the invention by way of illustration, but not by way of limitation, and represent like elements with the same reference numerals; all drawings are schematic, and only the components necessary to clarify the invention are generally disclosed; For simple and clear disclosure, the elements shown in the drawings and discussed below are not necessarily drawn to scale. Known structures and devices are shown in simplified form to avoid unnecessarily obscuring the invention; other parts can be omitted Or simply suggest. FIG. 1 shows a conventional condenser microphone in a conventional technique. FIG. 2A schematically illustrates a condenser microphone in a lateral mode according to an exemplary embodiment of the present invention. FIG. 2B shows a condenser microphone in a lateral mode according to an exemplary embodiment of the present invention. Figure 3 shows the sound pressure of a microphone hitting a range of directions. FIG. 4 shows a method for determining a main direction of an internal component in a microphone according to an exemplary embodiment of the present invention. FIG. 5 shows a micro-electro-mechanical condenser microphone according to an exemplary embodiment of the present invention. FIG. 6 shows a first / second electrical conductor having a comb structure according to an exemplary embodiment of the present invention. FIG. 7 illustrates a spatial relationship between two comb teeth in FIG. 6 according to an exemplary embodiment of the present invention. FIG. 8 shows four movable films arranged in a 2 × 2 array according to an exemplary embodiment of the present invention. FIG. 9 shows a design of one or more, for example, two air flow restrictors, according to an exemplary embodiment of the present invention. Figure 10 shows that the sensitivity of the microphone is reduced at low frequencies due to air leakage. FIG. 11 shows a frequency response with reduced / prevented air leakage according to an exemplary embodiment of the present invention. FIG. 12 illustrates a frequency response of a microphone design in a lateral mode according to an exemplary embodiment of the present invention. Figure 13 shows the frequency response of a comparison conventional microphone design.

Claims (20)

A condenser microphone includes a first conductive body and a second conductive body, which are configured to have a relative spatial relationship therebetween, wherein a mutual capacitance is generated between the first conductive body and the second conductive body. ; Wherein the relative spatial relationship and the mutual capacitance are both changed by a sound pressure that strikes the first electrical conductor and / or the second electrical conductor in a range along an impact direction in a three-dimensional space; Along the range of the collision direction, there is a sound pressure that strikes the first electrical conductor and / or the second electrical conductor along one of the directions, so that the mutual capacitance changes the most. The direction is defined as a Main direction; wherein the first conductor has a first projection along the main direction on a conceptual plane perpendicular to the main direction; wherein the second conductor has a first projection along the main direction on the conceptual plane A second projection; and wherein there is a shortest distance Dmin between the first projection and the second projection, and whether or not the first conductor and / or the second conductor are impacted by sound waves along the main direction Which is greater than the shortest distance Dmin 0. The condenser microphone according to claim 1, wherein the first conductor and the second conductor are independent of each other and made of polycrystalline silicon, gold, silver, nickel, aluminum, copper, chromium, titanium, or platinum. The condenser microphone according to claim 2 is a micro-electromechanical (MEMS) microphone. The condenser microphone according to claim 3, further comprising a substrate, wherein the substrate is the conceptual plane, and wherein the first conductive body and the second conductive system are arranged side by side on the substrate. The condenser microphone according to claim 4, wherein the first conductor is fixed relative to the substrate, wherein the second conductor includes a thin film, the thin film is movable relative to the substrate, and wherein the main direction is vertical On the film plane. The condenser microphone according to claim 5, wherein the movable film is disposed on the substrate through three or more such as four suspension members. The condenser microphone according to claim 6, wherein the suspension member comprises a foldable and symmetrical cantilever. The condenser microphone according to claim 5, wherein the first conductor comprises a first comb-teeth group, and wherein the movable film includes a second comb-teeth group surrounding a peripheral area of the film, and The two combs are staggered. The condenser microphone according to claim 8, wherein the second comb-tooth group is movable laterally relative to the first comb-tooth group and has a low air resistance in a gap between the film and the substrate. The condenser microphone according to claim 8, wherein the first comb tooth group and the second comb tooth group have exactly the same shape and size. The condenser microphone according to claim 10, wherein each comb tooth has a same width measured along the main direction, and the first comb tooth group and the second comb tooth group have a length along the main Position difference in direction. The condenser microphone according to claim 11, wherein the position difference along the main direction is one third of the width. The condenser microphone according to claim 5, wherein the movable film has a square shape. The condenser microphone according to claim 13, further comprising one or more of the movable films. The condenser microphone according to claim 14 includes four movable films arranged in a 2 × 2 array configuration. The condenser microphone according to claim 5, further comprising an air flow limiter for limiting the flow rate of air flowing in / out of the gap between the film and the substrate. The condenser microphone according to claim 16, wherein the air flow restrictor reduces an air passage size so that air flows into / out of the gap between the film and the substrate. The condenser microphone according to claim 16, wherein the air flow restrictor increases the length of the air passage so that air flows into / out of the gap between the film and the substrate. The condenser microphone according to claim 16, wherein the air flow restrictor includes an insert member inserted into a groove. The condenser microphone according to claim 5, further comprising at least two air flow restrictors for limiting the flow rate of air flowing in / out of the gap between the film and the substrate.